Conventionally, the inner and outer plates at the chain guide in the front derailleur are spaced at an interval larger than a width of the chain, and if the interval is too large, an amount of moving the chain guide should be increased for switching the chain, thereby creating a problem in that the control lever stroke becomes longer thus deteriorating the speed change efficiency. Hence, the interval is restricted by itself.
In a case where the conventional chain guide, as shown in FIG. 4, is used and the front and rear derailleurs are operated to switch the chain C from one of the multistage front gears FG to one of the multistage rear gears RG, the chain line of chain C inclines between the front chain gear FG and the rear one RG, especially largely between a low speed front chain gear FG.sub.1 and a high speed rear chain gear RG.sub.1, thereby creating a problem in that the chain C may come into contact with the outer plate of the chain guide at the front derailleur to generate sounds. Especially, when three front chain gears, or six rear chain gears, are used, the above trouble is often created.
Thus, it has been difficult to eliminate sound generation without sacrificing the speed change efficiency, whereby a chain guide superior in speed change efficiency and free from sound generation has earnestly been demanded.